A device for solar energy storage and release based on a reversible chemical reaction is demonstrated. A highly soluble derivative of a (fulvalene)diruthenium (FvRu2) system is synthesized, capable of storing solar energy (110 J g−1) in the form of chemical bonds and then releasing it “on demand”, when excited thermally or catalytically. A microfluidic device is designed and constructed for both the photo-harvesting and the heat-utilization steps, allowing for the recycling of material.